Roofing Terms

When you hear a roofing term that you don't understand, come to our easy to use glossary for help. Your new roof is a large investment you deserve to know and understand the terminology used by your builder, contractor, and suppliers.

A

Absorption: The act or process of retaining foreign particles, such as gas or liquid, without transmission of these particles.

ACI: American Concrete Institute

Acid Etch: (1) The use of a strong acid to remove the surface of concrete thereby exposing the aggregate. (2) The use of a strong acid to etch the surface of material such as metal in order for that material to accept a primer or Spray Polyurethane Foam (SPF).

ACIL: American Council of Independent Laboratories

Acrylic Coating: A coating system with an acrylic resin base.

Acrylic Resin: Polymers of acrylic or met acrylic monomers often used as a latex base for coating systems.

Active: Will corrode in the presence of moisture or a noble metal. (Noble metals being those that are resistant to corrosion and oxidation in moist air, unlike most base metals.)

Adhere: The clinging of one surface to another, either molecularly or otherwise.

Adhesion: The state of adhering.

AFA: American Fiberboard Association

AGC: Associated General Contractors of America

Aggregate: A surfacing or ballast for a roof system. Aggregate can be rock, stone, crushed stone or slag, water-worn gravel, crushed lava rock, or marble chips.

AHA: American Hardboard Association

AIA: American Institute of Architects

Air Blown Asphalt: Asphalt produced by blowing air through molten asphalt held at an elevated temperature. This procedure is used to modify properties of the asphalt.

Alligatoring: The cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks that resemble an alligator's hide.

Aluminized Steel: Sheet steel with a thin aluminum coating on the surface to enhance the steel's ability to withstand weathering.

Aluminum: A non-rusting metal used for metal roofing and the fabrication of gutter and flashings.

Ambient Temperature: The temperature of the air.

Anodic: When two metals are connected in an electrolyte, they will form a galvanic cell with the higher metal in the galvanic series being the anode. The anodic will oxidize and produce an electrical current that protects the cathode from corrosion.

ANSI: American National Standards Institute

APA: American Plywood Association

Application Rate: The rate at which a material is applied per unit area.

Apron Flashing: A flashing located at the low end of a curb or penetration.

Architectural Shingle: Shingle that provides a dimensional appearance. See also Dimensional Shingle.

Area Divider: A flashed assembly usually extending above the surface of the roof that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas.

ARMA: Asphalt Roofing Manufacturers Association

ASA: American Subcontractors Association

Asbestos: An incombustible fibrous mineral form of magnesium silicate formerly used for fireproofing and sometimes used for the reinforcement of roofing materials.

Asphalt: A substance left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt can be refined to conform to various roofing grade specifications:

Dead-Level Asphalt: A roofing asphalt conforming to American Society for Testing and Materials (ASTM) Specification D 312, Type I. This asphalt is for use in roofs that do not exceed a ¼ in 12 slope (2%). Flat Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type II. This asphalt is for use in roofs that do not exceed a ½ in 12 slope (4%). Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III. This asphalt is for use in roofs that do not exceed a 3 in 12 slope (25%). Special Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV. This asphalt is for use in roofs that do not exceed a 6 in 12 slope (50%).

Asphalt Emulsion: A mixture of asphalt particles and an emulsifying agent such as bentonite clay and water.

B

Back-Nailing: The method of fastening the back or upper side of a ply of roofing felt or other component in a roof system so that the fasteners are covered by the following ply.

Back-Surfacing: A fine mineral material on the back side of roofing materials such as roll roofing to keep them from sticking together while packaged.

Ballast: A material installed over the top of a roof membrane to help hold it in place. Ballasts are loose-laid and can consist of aggregate, or concrete pavers.

Bar Joist: See Steel Joist.

Barrel Roof: A roof configuration with a partial cylindrical shape to it.

Base Flashing (membrane base flashing): Plies of roof membrane material used to seal a roof at the vertical plane intersections, such as at a roof-wall and roof-curb junctures. See also Flashing.

Base Ply: The primary ply of roofing material in a roof system.

Base Sheet: An asphalt-impregnated, or coated felt used as the first ply in some built-up and modified bitumen roof systems.

Batten: (1) A strip of wood usually fastened to the structural deck for use in attaching a primary roof system such as tile. (2) A plastic strip, wood strip, or metal bar which is used to fasten or hold the roof and/or base flashing in place - also known as a Termination Bar.

Bermuda Seam: A metal roof that has a step profile.

Bird Bath: Small, inconsequential amounts of water on a roof that quickly evaporate.

Bird Screen: Wire mesh installed over openings in order to prevent birds from entering a building or roof cavity.

Bitumen: Any of various flammable mixtures of hydrocarbons and other substances, occurring naturally or obtained by distillation from coal or petroleum that are a component of asphalt and tar and are used for surfacing roads and for waterproofing.

Bitumen-Stop: A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered. See also Envelope.

Bituminous Emulsion: Bituminous particles suspended in water or other solution. See also Asphalt Emulsion.

Bleeder Strip: A starter strip placed along rake edges for use in asphalt shingle roofing. See also Rake-Starter.

Blind-Nailing: The use of nails so that they are not exposed to the weather in the finished roofing system. See Back-Nailing.

Blister: A pocket of air trapped between layers of felt or membrane - usually caused by water or other foreign substances.

Blocking: Pieces of wood built into a roof assembly used to stiffen the deck around an opening, support a curb, or for use as a nailer for the attachment of membranes or flashing.

Blown Asphalt: See Air Blown Asphalt.

Blueberry: A small bubble found in the flood coat of an aggregate-surfaced, built-up roof.

BOCA: Building Officials and Code Administrators, International, Inc.

BOMA: Building Owners and Managers Association, International

Bond: The force(s) holding two components in positive contact.

Bonding Agent: A chemical agent used to create a bond between two layers.

Boot: A piece of material preformed to protect roof penetrations from dirt, moisture, and other foreign and/or damaging substances.

Brake: A piece of equipment used for forming metal.

Bridging: When membrane is unsupported at a juncture.

British Thermal Unit (BTU): The heat energy necessary to raise the temperature of one pound of water one degree Fahrenheit - equivalent to a joule.

Brooming: Embedding a ply of roofing material into hot bitumen or adhesive by using a broom, squeegee, or other piece of equipment to eliminate voids and help ensure adhesion.

Buckle: A long, tented displacement of a roof membrane. Can occur over insulation and deck joints.

Built-Up Roof Membrane: A roof membrane consisting of layers of bitumen, which serves as the waterproofing component, with plies of reinforcement fabric installed between each layer. The reinforcement material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate, emulsion or a granule-surfaced cap sheet.

Bundle: An individual package of shingles or shakes.

BUR: An acronym for Built-Up Roof. See Built-Up Roof.

Butadiene: A colorless, highly flammable hydrocarbon, C4H6, obtained from petroleum and used in the manufacture of synthetic rubber.

Butt Joint: Where two separate, adjacent pieces of material abut.

Butyl: A hydrocarbon radical, C4H9. Butyl has a rubber-like consistency, is formed from the copolymerization of isobutylene and isoprene and is used primarily in sealants and adhesives.

Butyl Rubber: A butyl-based, synthetic elastomer.

Butyl Tape: A sealant tape used in numerous sealant applications such as sealing sheet metal joints.

C

Calender: A machine used to laminate sheeting or for applying coating with a specified thickness and/or surface attribute.

Calendering: A specific process used to manufacture some membranes such as PVC.

Camber: A slight convex curve of a surface.

Canopy: An overhang, usually over entrances or driveways.

Cant: (1) Short for Cant Strip. (2) The act of installing foam at a right angle adjunct.

Cant Strip: A triangular-shaped strip of material used to ease the transition from a horizontal plane to a vertical plane. Cant strips can be made of wood, wood fiber, perlite, or other materials.

Cap Flashing: A material used to cover the top edge of base flashings or other flashings. See also Coping.

Cap Sheet: A granule-surfaced membrane often used as the top ply of BUR or modified roof systems.

Capacitance Meter: A device for locating moisture within a roof system by measuring the ratio of the change to the potential difference between two conducting elements that are separated by a non-conductor.

Catalyst: A substance that effects a chemical reaction and/or the rate at which a chemical reaction takes place. In roofing, catalysts are used in SPF roofing.

Cathodic: Metals low in the Galvanic Series.

Caulk: A material with no elastomeric properties used for sealing joints.

Caulking: The act of sealing a joint or of material.

Cavitation: The vaporization of a liquid under the suction force of a pump which can create voids within the pump supply line. Cavitation will result in off-ratio foam in Sprayed Polyurethane Foam applications.

CCF: 100 cubic feet.

C-Channel: A structural framing member that, when viewed cross-sectionally, has the shape of a "C."

Cellulose: A complex carbohydrate, (C6H10O5)n, that is composed of glucose units, forms the main constituent of the cell wall in most plants, and is used in the manufacturing of organic roofing materials.

CERL: Construction Engineering Research Laboratory

CG&E: See Chopped Glass and Emulsion.

Chalk: A powdery residue on the surface of a material.

Chalk Line: (1) A string on a reel in a container that can hold chalk. (2) A line made on by pulling taut a string coated with chalk and snapping it.

Channel Flashing: Flashing with a built-in channel for runoff; used where roof planes intersect other vertical planes.

Chemical Resistance: A materials ability to retain its properties when it comes into contact with certain chemicals.

Chlorinated Polyethylene1 (CPE): CPE is a flexible material with high tear strength, good chemical resistance and patency towards UV radiation. As a result of the high chlorine content (typically 30%) it is inherently difficult to ignite, but releases hydrogen chloride during combustion. It suffers from an extremely high permeability to gas. Resistance to most inorganic chemicals is generally good, while resistance to hydrocarbons increases with increasing chorine content. The material is used mainly as an impact modifier for PVC and, to a lesser extent, LDPE and HDPE film.

Chlorosulfonated Polyethylene (NRCA Definition): A synthetic, rubber-like thermoset material, based on high molecular weight polyethylene with suphonyl chloride, usually formulated to produce a self-vulcanizing membrane. Chlorosulfonated Polyethylene or CSPE. Best know as Hypalon™, it was developed in 1951 by DuPont.

Chopped Glass and Emulsion (CG&E): A roof coating that consists of asphalt or clay emulsion and glass fiber reinforcement. The glass fiber comes in rope form and is mechanically chopped into small pieces and then mixed with the emulsion at the end of the spray gun so that the mixture is complete by the time the surfacing hits the top of the roof. Standard mixture is 9 gallons of emulsion and 3 pounds of glass fiber for every 100 square feet (36.5 Liters of emulsion and 1.5 kg of chopped glass for every 10 square meters). The CG&E coating is then usually surfaced with a fibered aluminum roof coating at rate of 1.5 gallons per 100 square feet (6 Liters per 10 square meters).

Cladding: A material used to cover the exterior wall of a building.

Cleat: A continuous metal strip used to secure two or more metal roof components together. Commonly used along with coping or gravel stop on tall buildings.

Clerestory (Clearstory): A room that extends above an abutting roof section of a building.

Clip: A small cleat.

Clipped Gable: A gable cut back at the ridge in a small hip configuration.

Closed-Cut Valley: A method of valley application in which shingles from one side of the valley extend across the valley while shingles from the other side are installed over the top of those and then trimmed back approximately 2 inches from the valley centerline.

Closure Strip: A material used to close openings created by joining metal panels or sheets and flashings.

Coal Tar Bitumen: A proprietary trade name for Type III coal tar used in dead-level or low-slope built-up roofs. It is not for use in roofs exceeding ¼ in 12" (2%) slope.

Coal Tar Pitch: A type of coal tar used in dead-level or low-slope built-up roofs. It is not for use in roofs exceeding ¼ in 12" (2%) slope.

Coarse Orange Peel Surface Texture: A surface showing a texture where nodules and valleys are approximately the same size and shape. This surface is generally acceptable for installing a protective coating.

Cold Process Built-Up Roof: A roof consisting of multiple plies of roof felts laminated together with adhesives that usually come right out of a can or barrel and require no heating.

Collector Head: A component used to direct water from a through-wall scupper to a downspout. Also known as a Conductor Head.

Column: A vertical structural member placed on a footing or foundation used to support horizontal above-ground building components.

Combing Ridge: A term used to describe an installation of finishing slate at the ridge of a roof whereby the slates on one side project beyond to the apex of the ridge.

Combustible: Capable of igniting and burning.

Composition Shingle: A type of shingle used in steep-slope roofing and generally comprised of weathering-grade asphalt, a fiberglass reinforcing mat, an adhesive strip, and mineral granules.

Compounded Thermoplastics1 (NRCA Definition): A category of roofing membranes made by blending thermoplastic resins with plasticizers, various modifiers, stabilizers, flame retardants, UV absorbers, fungicides, and other proprietary substances, alloyed with proprietary organic polymers. Some of the membranes listed in this generic category are CPA, EIP, NBP, and TPA.

Concealed-Nail Method: A method of installing asphalt roll roofing material in which all nails or fasteners are driven into the underlying roofing and covered by an overlapping course.

Condensate: The liquid resulting from condensation.

Condensation: The conversion of water vapor to liquid state when warm air comes in contact with a cold surface. See also Dew Point.

Conduction: The transmission or conveying of something through a medium or passage, especially the transmission of electric charge or heat through a conducting medium without perceptible motion of the medium itself.

Conductor Head: A component used to direct water from a through-wall scupper to a downspout. Also known as a Collector Head.

Construction Joint: A constructed joint where two successive installments of concrete come together.

Contact Cements: Adhesives used to adhere or bond roofing components.

Coping: The piece of material used to cover the top of a wall and protect it from the elements. It can be constructed from metal, masonry, or stone.

Copper: A reddish-brown element that conducts heat and electricity very well. It is also used as a primary roof material as well as a flashing component. Copper turns a greenish color after being exposed to the weather for a length of time and appears in the middle of the Galvanic Series.

Cornice: A horizontal projecting part that crowns the wall of a building.

Counterflashing: Formed metal sheeting secured to walls, curbs, or other surfaces, for use in protecting the top edge of base flashings from exposure to weather.

Course: (1) The term used for each row of roofing material that forms the roofing or flashing system. (2) One of multiple layers materials applied to a surface. For example, a three-course flashing consists of a layer of mesh or other reinforcing material sandwiched between two layers roofing cement.

Cove: In roofing, a heavy bead of sealant material installed at the point where vertical and horizontal planes meet. It is used to eliminate the 90º angle. See also Fillet.

Cover Plate: A metal strip sometimes installed over the joint between formed metal pieces.

Coverage: The surface area covered by a material.

CPA: Copolymer Alloy.

CPE: Chlorinated Polyethylene.

Crack: A separation or fracture occurring in a material.

Cream Time: Time in seconds at a given temperature when the A and B (isocyanate and resin) components of SPF will begin to expand after being mixed.

Creep: Movement of roof membrane causing the roof system to be deformed.

Cricket: A roof component used to divert water away from curbs, platforms, chimneys, walls, or other roof penetrations and projections. See also Saddle.

Cross Ventilation: The effect of air moving through a roof cavity between vents.

CRREL: Cold Regions Research and Engineering Laboratory

Crow's Nest: See Cupola.

CSI: Construction Specifications Institute

CSM: ASTM designation for Chlorosulfonated polyethylene. See CSPE.

CSPE: Chlorosulfonated polyethylene.

Cupola: A relatively small roofed structure set on the ridge of a main roof area. Also known as a Crow's Nest.

Curb: (1) A raised member used to support skylights, HVAC units, exhaust fans, hatches or other pieces of mechanical equipment above the level of the roof surface, should be a minimum of eight inches (8") in height. (2) A raised roof perimeter that is relatively low in height.

Cure: A process by which a material is forms permanent molecular linkages by exposure to chemicals, heat, pressure, and/or weathering.

Cure Time: The time necessary to effect curing.

Curing Agent: A material additive that alters chemical activity between the components resulting in a change in the rate of cure.

Curing Compound: A liquid that is applied to newly installed concrete that slows water loss while curing.

Cutback: Bitumen thinned by solvents that is used in cold-process roofing adhesives, roof cements, and roof coatings.

Cut-off: A detail designed to seal and prevent lateral water movement in an insulation system, and used to separate different sections of a roofing system.

D

Dampproofing: Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead Level: Refers to a roof with no slope or pitch.

Dead-Level Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I. This asphalt is for use in roofs which do not exceed a ¼ in 12 slope (2%).

Dead Loads: Permanent, non-moving loads on a roof resulting from the weight of a building's components, equipment, and the roof system.

Deck: The structural component of the roof of a building that provides the substrate to which the roofing system is applied.

Decking: See Deck.

Deflection: The downward displacement of a structural member under load.

Degradation: A decline in the appearance, structure, or properties, of a material or substance.

Delamination: Separation of laminated layers of a material or system.

Dew Point Temperature: The temperature at which water vapor turns to liquid in cooling air at the existing atmospheric pressure and vapor content.

Diaphragm: A type of structural roof deck capable of resisting shear that is produced by lateral forces such as wind or seismic loads.

Diffusion: The movement of a substance such as water vapor from regions of high concentration to regions of lower concentration.

Dimensional Shingle: A shingle that is textured, or laminated to produce a three-dimensional effect. Also known as Laminated and Architectural Shingles. Please be aware that there are also shingles being produced that can be classified as Dimensional but not as Laminated. These shingles are comprised of a single piece of material rather than two different materials laminated together.

Dimensional Stability: The ability of a material to retain its current properties and to resist a change in size resulting from exposure to temperature changes and moisture.

Dome: A roof with a partial-spherical shape.

Dormer: A framed projection through the sloping plane of a roof.

Double Coverage: Installing roofing so that there is twice the materials used resulting in a double layer of roofing.

Double Graveling: Installing one layer of gravel in a flood coat of hot bitumen, removing the excess gravel and then installing a second layer of gravel in another flood coat of hot bitumen.

Downspout: A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as a Leader Pipe.

Drain: a device used to carry water off of a roof.

Drip Edge: A steel flashing bent at a 90º angle that is placed along the outer perimeter of steep sloped buildings; used to help direct runoff water away from the building. Drip Edge resembles nosing except that it has an outwardly-angled bottom edge (preferably hemmed).

Dry Bulb Temperature: The temperature of air in degrees Fahrenheit measured by an ordinary thermometer.

Dry Film Thickness: The thickness in mils (thousandths of an inch), of a dried coating or mastic.

Dry-In: (1) The process of installing the underlayment in steep slope roofing. (2) Making a low-slope roof watertight. Does not always mean getting all of the required plies installed.

Dry Rot: Wood rot caused by certain fungi. Dry rot can result from condensation build-up, roof leaks that go untended, or from other problems. Dry rot will not remain localized. It can spread and damage any lumber touching the affected area.

Dual Level Drain: An item that will permit drainage at two different levels.

Dynamic Load: Any moving load on a roof such as people and equipment. Wind can also be considered a Dynamic Load.

Edge Venting: The installation of vent material along a roof edge (e.g., Starter Vent) as part of a ventilation system. Edge vent material should be used in conjunction with other venting material (e.g., ridge vent) as it not intended for use by itself.

Elastomer: A material which, after being stretched, will return to its original shape.

Elastomeric: Properties of a material that will permit it to return to its original shape after being stretched.

Elastomeric Coating: A coating that can be stretched to twice its dimensions and that will return to original when tension is released.

Elongation: The ability of a material to be stretched or lengthened.

Embedment: In roofing, to uniformly press one material into another, such as aggregate into bitumen, roofing felt into bitumen, or granules into a coating.

Emulsion: Fine particles suspended in a liquid solution. See also Asphalt Emulsion

End Lap: The extension of one component of material past the end of an adjacent piece of material.

Envelope: A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered.

EPDM: Ethylene Propylene Diene Monomer.

Epichlorohydrin (ECH): A synthetic rubber material similar to EPDM with a stronger resistance to animal fats and oils than EPDM.

Equipment Screen: A nonstructural wall or screen constructed around rooftop equipment such as HVAC units, curbs, etc. to hide the look of the equipment and make the structure more aesthetically pleasing.

Equiviscious Temperature (EVT): The temperature at which a bitumen attains the proper viscosity for use in built-up roofing. There is usually a twenty-five degree Fahrenheit (25º F) variance permitted above and below the recommended EVT. The EVT is measured in application equipment just prior to application using a standard thermometer or it can be measured just after application using a laser thermometer.The following tables have SAMPLE EVT temperatures.

F

Factory Mutual Research Corporation (FMRC): As it relates to roofing - a division of Factory Mutual System that tests and classifies roof components and systems for their resistance to fire, traffic, impact, weathering, and wind-uplift. The various organizations of Factory Mutual are owned or directed by Allendale Insurance, Arkwright, and Protection Mutual Insurance.

Factory Seam: A splice/seam made in the roofing material by the manufacturer. It is preferable during installation to cut these splices out of the membrane.

Fading: Losing brightness or brilliance-dim.

Fallback: A reduction in the softening point temperature of asphalt that occurs when asphalt is overheated for pro-longed periods of time.

Fascia: Vertical roof trim located along the perimeter of a building, usually below the roof level. Its use can be either decorative or for waterproofing.

Fasteners: Devices used to secure roof system components.

Feathering Strips: Strips of wood that are placed along the butt ends of wood shingles to form a somewhat smooth surface so that the shingles can be roofed over without removal.

Felt: A roofing sheet made of interwoven fibers. The fibers can be wood or vegetable for Organic Felts, glass fibers for fiberglass felts, polyester, or asbestos.

Felt Machine: A machine that will install bitumen and felt at the same time.

Ferrule: A metal sleeve used as a spacer to keep gutter from being beat up when secured to fascia with spikes.

Fiberglass Insulation: Insulation composed of glass fibers used to insulate walls and roofs. It can be rigid board or blanket insulation.

Field of the Roof: Refers to the central part of a roof away from the perimeter.

Field Seam: A non-factory material seam made by joining overlapping seams together with adhesives, heat welders, or other means.

Filler: An inert ingredient added to roofing materials in order to alter their physical characteristics.

Film: A membrane or sheeting material with a nominal thickness of 10 mils or less.

Film Thickness: The thickness of a membrane or coating that is expressed in mils (thousandths of an inch).

Fin: A sharp protrusion in a roof deck that can damage roof components.

Fine Mineral-Surfacing: A fine mineral material on the surface of roofing materials to prevent them from sticking to surfaces. 50% of this material has to pass through a sieve with holes that are 1/35" in size (#35 sieve).

Fishmouth: An opening along the exposed edge of an installed ply of felt caused by shifting the ply during installation. Repair these by making a slice along their entire length and feathering two plies of felt over the fishmouth for a minimum coverage of one foot all the way around.

Flaking: Occurs when a coating loses its cohesion.

Flame Retardant: A substance used to impede a material's tendency to burn or ignite.

Flange: A projection edge of a roof component such as flashings, skylight frames, pre-manufactured curbs, etc. Usually refers to the part that sits on the roof surface.

Flash: To install flashing components.

Flash Point: The lowest temperature of a liquid material at which combustion will occur when air reaches its surface.

Flashing: Components used to seal the roof system at areas where the roof covering is interrupted or terminated. For example, pipes, curbs, walls, etc. all have special components that, when correctly installed, will help prevent moisture entry into the roof system or building.

Flashing Cement: A trowelable mixture of solvent-based bitumen and mineral stabilizers. Flashing cement that may contain asbestos stabilizers is categorized by ASTM standard D 2822-91 (1997) or for non-asbestos, ASTM standard D 4586-93. Flashing Cement is the term for Asphalt Roof Cement that can be used on vertical surfaces and has a high softening point, low ductility and conforms to the requirement of ASTM Specification D 312, Types II or III; or Specification D 449, Type III. See also Asphalt Roof Cement and Plastic Cement.

Flat Lock: A type of interlocking two separate metal panels by folding one panel over on top itself and the folding the other down under itself and then hooking the panels together.

Fleece: Mats or felts used as a membrane backer and composed of fibers.

Flood Coat: The surfacing layer of bitumen into which aggregate is embedded on an aggregate-surfaced built-up roof. A flood coat is applied at an approximate rate of 45 to 60 pounds per square (100 square feet).

Flood Test: A water test performed to determine the effectiveness of a roof covering.

Flow: To become fluid in character.

Fluid-Applied Elastomer: A liquid elastomeric material that cures to form a continuous waterproofing membrane.

G

G-90: A coating weight for galvanized sheet metal, 0.90 ounces of zinc per sq. ft., measured on both sides of the sheet.

Gable: A triangular-shaped portion of the endwall of a building directly under the sloping roof and above the Eave line.

Gable Roof: A roof configuration that has gable ends.

Gable-On-Hip Roof: A roof configuration with hips coming up from the eave corners that terminate into a gable roof.

Galvalume: Trade name for a protective coating composed of aluminum zinc.

Galvanic Action: A reaction between different metals in the presence of an electrolyte.

Galvanize: To coat with zinc.

Galvanized Steel: Steel that is coated with zinc to aid in corrosion resistance. Galvanized steel for use in roofing should be Hot-Dipped Galvanized with a G-90 coating.

Gambrel: A roof that has two different pitches.

Gauge: A standard of measurement. For instance the thickness of sheet metal or the diameter of wire. The thicker the wire or metal, the lower the gauge.

Geodesic Dome: A geodesic dome uses a pattern of self-bracing triangles in a pattern that gives maximum structural advantage, thus theoretically using the least material possible. (A "geodesic" line on a sphere is the shortest distance between any two points.) The first contemporary geodesic dome on record was designed by Walter Bauersfeld.

Girt: A horizontal beam place between support columns that is used for attaching wall cladding.

Glass Felt: (1) In the manufacturing of roofing materials - a sheet comprised of bonded glass fibers prior to being saturated with bitumen. (2) short for asphalt or coal tar saturated fiberglass felt membrane.

Glaze Coat: (1) The uppermost layer of asphalt on a smooth-surfaced built-up roof membrane, usually a reflective surfacing is installed over it. (2) A thin coat of bitumen applied to help protect the roof membrane when application of additional felts or the flood coat and aggregate surfacing are delayed.

Grain: A unit of measure for the mass of moisture: a unit of weight equal to 0.002285 ounces or 0.036 dram.

Granule: A small aggregate, naturally or synthetically colored, used to surface cap sheets, shingles, and other granule-surfaced roof coverings.

Gravel: Aggregate consisting of rock fragments or pebbles.

Gravel Stop: A flanged, sheet metal edge flashing with an upward projection installed along the perimeter of a roof to stop the flow of bitumen over the edge.

Grout: A thin mortar used to fill cracks in masonry and tile.

Grout (Non-Shrink): A cementitious material used to partially fill penetration pockets (pitch pans). A pourable sealer is used afterward.

Gutter: A channel (usually sheet metal) installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.

I

ICBO: International Conference of Building Officials, responsible for The Uniform Building Code.

Ice Dam: Ice formed at the transition from a warm surface to a cold surface, such as along the overhang of a house. The build-up of ice is the result of ice or snow melting on the roof area over the warmer, living area of a building and then refreezing when it runs down and reaches the overhang.

Ignition Temperature: The minimum temperature at which a material will combust.

Impact Resistance: A roof assembly's ability to withstand the impact from falling objects such as hail.

Impregnate: To saturate; in roofing, asphalt impregnated fiber glass roofing felts are fiber glass mats that have been completely permeated with asphalt bitumen.

Infrared Thermography: The use of an infrared camera to detect moisture in roof insulation.

Insect Screen: Material used to inhibit an insects ability to enter a building through openings in a roof such as vents.

Insulation: Material used to help maintain a certain temperature in a building by reducing the flow of heat to and from that building. See also Thermal Insulation.

Intake Ventilation: The part of a ventilation system used to draw fresh air in. Usually vents installed in the soffit or along the eaves of a building.

Interlayment: A waterproof material usually installed between adjacent rows of wood shakes to help with the roof's waterproofing characteristics.

Interlocking Shingles: Shingles that lock together to provide wind resistance. See also T-Lock.

Internal Pressure: Atmospheric pressure inside a structure that correlates to the number and location of openings and air leaks.

Inverted Roof Membrane Assembly (IRMA®): A variation of the "Protected Membrane Roof Assembly" in which Styrofoam® brand insulation is used. IRMA® and Styrofoam® are registered trademarks of the Dow Chemical Company.

K

L

Laitance: An accumulation of fine, powdery aggregate particles on fresh cement caused by the upward movement of water - indicates that too much water was used in the mix resulting in poor surface adhesion for a waterproofing layer.

M

Mansard: (1) A steep-sloped roof located at the perimeter of a building and usually used for decorative purposes. (2) The upper story formed by the lower slope of a mansard roof.

Mansard Roof: A steeper roof that terminates into a lower sloped roof at its high point.

Masonry: Refers to bricks, concrete, or concrete blocks.

Mastic: See Asphalt Roof Cement.

Mat: A thin layer of woven, non-woven, or knitted fiber used to reinforce a material.

Material Safety Data Sheets (MSDS): Written descriptions of the chemicals in a product provided by the product's manufacturer. MSDS also contain other information such as emergency procedures and safe handling.

MBMA: Metal Building Manufacturers Association

MCA: Metal Construction Association

Mechanical Damage: Damage to a roof by means of items puncturing or otherwise unnecessarily penetrating the roof system or any of its components. Screws or nails stuck in the roof and heel marks along base flashings are examples of mechanical damage.

Mechanical Fasteners: Devices such as screws, plates, battens, nails, or other materials that are used to secure roofing materials.

Membrane: The portion of the roofing system that serves as the waterproofing material. Can be composed of one material or several materials laminated together.

Metal Flashing: Roof components made from sheet metal that are used to terminate the roofing membrane or material along roof edges. Metal flashings are also used in the field of the roof around penetrations.

Meter: A metric unit of length measurement equal to 39.37 inches.

Mil: A unit of measure equal to 0.001 inches (1/1000 in., or one one-thousandth of an inch) used to indicate the thickness of a roofing membrane.

Mildew: A superficial coating or discoloration of organic materials caused by fungi, especially under damp conditions.

Millimeter: A metric unit of measure equal to one one-thousandth (0.001) of a meter, or 0.03937 inches.

MIMA: Mineral Insulation Manufacturers Association

Mineral Fiber: Inorganic fibers of glass or rock.

Mineral Granules: See Granules.

Mineral-Surfaced Roofing: Roofing materials with a top surface consisting of mineral granules.

Miter: The joint made by two diagonally cut pieces put together.

Model Codes: A group of codes and standards accepted by more than one of the Building Code regulatory agencies such as Southern Building Code Congress International (SBCCI), Building Officials and Code Administrators (BOCA), and the International Conference of Building Officials (ICBO).

Modified Bitumen: A bitumen modified by one or more polymers such as Atactic Polypropylene (APP), styrene butadiene styrene (SBS).

Moisture Relief Vent: A vent installed through the roofing membrane to relieve moisture vapor pressure that has been trapped within the roofing system.

Moisture Scan: A survey of a roof specifically to detect the amount of moisture present in the roof system. Devices used in moisture surveys can be capacitance meters, infrared cameras, and nuclear scanners. Infrared scans can be done from the air or on the surface of the roof. Capacitance and nuclear scans are done on the roof surface. It is argued that the most accurate scans are done from the surface of the roof with the most accurate of these being nuclear scans.

Mole Run: A term used to describe a ridge in a roof membrane that is not the result of improper deck or insulation joints.

Monolithic: Used to describe something without seams; formed from a single material.

Monomer: A simple molecule that can combine with other to form a polymer.

Mop-and-Flop: A roofers' term where the back side of a roofing material is mopped, then the piece is turned over and set in place.

Mopping: To apply hot asphalt or coat tar using a hand mop or mechanical applicator.

Mud Cracking: Surface cracking of a material that looks similar to dried, cracked mud.

Multiple Coats: More than one layer of coating applied to a substrate.

N

NAHB: National Association of Home Builders

Nailer: A piece of lumber, preferably treated, that is secured to the deck, walls, or to premanufactured curbs. Nailers are used to receive fasteners for roof membranes. Generally, nailers are installed wherever it is necessary to secure base flashings and edge metal.

Nailing Pattern: Refers to a specific method or pattern at which nails are applied. For instance, a nailing pattern for base sheets on plywood roof decks can be "Nine and Eighteen". This means one row of nails on the outside edge of the sheet set at nine inches (9") on center, and two rows in the center of the sheet, each set at eighteen inches (18") on center.

Neoprene: A synthetic rubber produced by polymerization of Chloroprene for use in liquid-applied and sheet-applied elastomeric roofing.

Nesting: To overlay existing shingles with new shingles and butt the top edge of the new shingle up against the bottom edge of the existing shingles.

Net Free Vent Area: The area permitting unrestricted air flow.

Newton (N): In the meter-kilogram-second system, the unit of force required to accelerate a mass of one kilogram one meter per second per second (s²).

NICA: National Insulation Contractors Association

Night Seal: To temporarily seal the edge of a roof membrane in order to protect it from moisture entry. Also known as Night Tie-Off and Water Cut-Off.

Ninety-Pound: Granule-surfaced, fiberglass, or organic felt roll roofing that has a mass of approximately 90 pounds per 100 square feet.

NIST: National Institute of Standards and Technology

Noble: In reference to metal, inert, or inactive.

No-Cutout Shingle: A shingle made of one solid strip of material.

Non-Breathing Membrane: A membrane that does not permit water vapor or air to permeate it.

Non-Flammable: Material with no measurable flash point.

Non-Friable: Refers to a material's inability to be crushed or pulverized into a powder.

Non-Volatile Content: The portion of a material that will not evaporate.

Non-Vulcanized Material: A material that retains its thermoplastic properties throughout its service life.

Nonwoven: Random arrangement of the reinforcement fibers of a scrim sheet or mat.

Nosing: Metal flashing bent at a 90º angle and is installed around roof perimeters, curbs, platforms, etc. in order to protect the edge of the roofing system. Nosing should not be used in place of drip edge.

P

Pan: (1) The concave piece of "Pan and Cover" tile whose rounded surface touches the top side of the roof substrate. (2) The flat part of a roofing panel located between the ribs.

Pan Flashing: A sheet metal flashing that covers an equipment platform and is designed to counter flash the base flashings surrounding the platform.

Parapet Wall: That part of a perimeter wall that extends above the surface of the roof.

Pass: The term used to describe the application of one layer of Spray Polyurethane Foam (SPF). The speed of a pass will determine foam thickness.

Pass Line: The distinct line formed between two passes of Spray Polyurethane Foam (SPF). This line is the top skin of the bottom pass of the SPF.

Penetration: Any object that pierces the surface of the roof.

Percent Elongation: The maximum amount that a material can be lengthened or stretched before breaking; expressed as a percentage of the original length of material tested.

Perlite: A natural volcanic glass having distinctive concentric cracks and a relatively high water content. In a fluffy heat expanded form, it is used in lightweight insulating concrete, fire-resistant rigid insulation board (R = 2.78 per inch) and potting soil.

Perm: A unit of water vapor transmission, defined as one grain of water vapor per square foot per hour per inch of mercury (Hg) pressure difference (1 inch of mercury = 0.491 psi).

Permeability: The rate of flow of a liquid or gas through a porous material.

pH: A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

Phasing: Installing roof system components in separate time intervals. For instance, installing a base sheet, and then two plies of roofing one day, and coming back and installing the remaining two plies one or more days later. It is generally not considered Phasing if the surfacing is applied at a later date.

Picture Framing: Rectangular patterns seen in a roof that are created by buckles or ridges in the roof system or sumps in the substrate.

PIMA: Polyisocyanurate Insulation Manufacturers Association

Pinhole: A small hole in a coating, foil, membrane, or other roofing material.

Pipe Boot: A prefabricated flashing piece used to flash around circular pipe penetrations. Also known as a Roof Jack.

Pitch: Term used to describe Roof Slope and also short for Coal Tar Pitch.

Pitch Pocket (also known as Pitch Pan): A flanged piece of flashing material placed around irregularly shaped roof penetrations and filled with grout and a pourable sealer to seal around the penetration in order to seal it from against moisture entry. Pitch pockets are a good source of leaks and should be avoided if possible.

Pittsburgh Lock Seam: A method of interlocking two separate pieces of metal.

Plastic Cement: A term used to describe Type I asphalt roof cement. Plastic cement should not be used on vertical surfaces. See also Asphalt Roof Cement and Flashing Cement.

Plastic Film: A flexible sheet made by the extrusion of thermoplastic resins.

Plasticizers: Material incorporated into rubber and plastic in order to increase their flexibility and workability.

Plenum: A space or enclosure in which air or other gas is at a pressure greater than that of the outside atmosphere.

Ply: A layer of felt or other reinforcement material in a roof system.

PMR: See Protected Membrane Roof.

Polyester: Any of numerous synthetic polymers produced chiefly by reaction of dibasic acids with Dihydric alcohols and used primarily as light, strong, weather-resistant resins. In roofing, polyester is used to reinforce fabrics.

Polymer: Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.

Polypropylene: Any of various thermoplastic resins that are polymers of propylene. They are hard, tough, and used to make molded articles and fibers.

Polyvinyl Chloride (PVC): A thermoplastic polymer that can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers, and other modifiers; rigid forms are used in pipes; flexible forms are used in the manufacture of sheeting and roof membrane materials.

Ponding: The accumulation of water at low-lying areas on a roof.

Pop Rivet: A small metal pin having a head on one end, inserted through aligned holes in pieces of light gauge metal to be joined and then the head is expanded to join the metal.

Positive Drainage: The drainage condition of a roof where all water is gone from the roof surface within forty-eight hours of precipitation during normal drying conditions.

Pot Life: The period of time during which a material with multiple ingredients can be applied or administered after being mixed together.

Pourable Sealer: A type of sealant that is initially in liquid form commonly used in conjunction with pitch pans to form a watertight barrier around penetrations that are difficult to flash.

Press Brake: A mechanical device used to form sheet metal into desired shapes and profiles.

Primer: A material that is applied to a surface in order to increase that surface's ability to adhere to or work in conjunction with a subsequently applied material.

Proportioner: A pumping unit comprised of two (2) positive displacement pumps that is designed to dispense two (2) components at a precise ratio. Used in SPF and plural component coating applications.

Protected Membrane Roof (PMR): A roof assembly in which the insulation and ballast are placed on top of the membrane component. Commonly referred to as an "inverted roof assembly."

Psychrometer: An instrument that uses the difference in readings between two thermometers, one having a wet bulb and the other having a dry bulb, to measure the moisture content or relative humidity of air.

Puncture Resistance: The ability of a material to withstand being pierced by a sharp object.

Purlin: Horizontal secondary structural member used to transfer loads from the primary structural members.

Q

R

R-Value: The measure of a material's resistance to heat flow. The higher a material's R-value, the more it insulates. For more information on R-Value, click on the term.

Racking: The method of installing asphalt shingles where the shingles are installed straight up to the ridge rather than horizontally. If this method is used with 3-tab shingles, the throats of every other course will line up.

Rafter: The structural member extending from the downslope perimeter of a roof to the ridge or hip and is designed to support the roof deck and roof system components.

Raggle: A groove that is cut into the side of a vertical surface such as a wall or chimney that is used to insert a flashing element such as a reglet or counterflashing.

Rake: The sloped perimeter edge of a roof that runs from the eaves to the ridge. The rake is usually perpendicular to the eaves and ridge.

Rake-Starter: A starter strip placed along rake edges for use in asphalt shingle roofing. See also Bleeder Strip.

RCI: Roof Consultants Institute

RCMA: Roof Coatings Manufacturers Association

RDCA: Roof Deck Contractors Association

Re-Cover (Overlay): The installation of a new roof system over an existing system without removing an existing system.